Hot-mill structure and operation



Jan. '29, 1929.

w. R. KNEELAND HOT MILL STRUCTURE AND OPERATION Filed March 17, 1927 2 Sheets-Sheet w41; PLN la (l-Qq Yr QQ, f, 0'@

Jan. 29, 1929. 1,700,267

w. R. KNEELAND HOT MILL STRUCTURE AND OPERATION Filed March 17, 1927 2 Sheets-Sheet 2 )NVENTOR K. ,Mumia Q JATQYQQQ (lifts.

Patented Jan. 2'9, 1929.

UNITED STATES WALTER R. KNEELANI)7 0F PITTSBURGH, PENNSYLVANIA.

HOT-MILL STRUCTURE AND OERATION.

Application led March 17, 1927. Serial No. 5.761081.

lily invention relates to improvements in hot-mill structure and operation. The objects in view are diminution of loss due to the breakingl oit' rolls, improvement in the quality of and particularly in the uniformity in the thickness of the rolled material, and enlarging the practical limits upon the size to which the sheets of material may be rolled. The gaining of these ends effects obvious improvements in product and economies of operation.

ln the accompanying drawings Fig. I is a view in elevation and Fig. Il a view in plan of a hot-mill in which and in the operation of which my invention is embodied and achieved. Fig. lll is a diagrammatic view, in which the rolls of the mill are indicated, in position corresponding to Fig. l, and certain shields in which my present invention is in part embodied are shoivn in vertical and transverse section. Figs. IV, V, and Vl show one of the shields in detail; Fig. IV is a View of the shield in rear elevation, Fig. V a view in approximately horizontal and medial section. (indicated at V--V, Fig. IH) and Fig. VlY a vieiv in front elevation.

A het-mill is a steel mill for rolling light plates and sheets of steel.. lts characteristic is that during the rolling operation its rolls are not. as are the rolls of a plate mill, cooled by streams of Water poured upon them. In preparation for the rolling operation the rolls are heated te a temperature approximating, though somewhat less than, the temperature of the material to be rolled; and the heat which the rolls in the progress of the rolling operation take up, is given ed again merely by ra diation to the surrounding air. A typical procedure in hot-mill operation as hitherto practi ed. is as follows: From forty to iifty bars cut to proper length are charged into a e furnace. These bars are for ordinary sheet rolling` for tinning, uniformly 8 inches Wide. Their length is that of the width of the ultimate sheet, and this for practical reasons presently to be considered has hitherto been limited to 28 inches. The bars vary in thickness from to 5/q of an inch, according to the length desired for the rolled sheet.

The heated bars are taken from the furnace twc al a time and are entered singly into the mill. They pass through the mill singly. each from four to siX times. These are called the roughing passes. The roughed hars are introduced into a second heating furnace, from which when heated they are taken two by tivo, matched, and passed twice through the mill. These passes which constitute the second rolling` step are called the matching passes or the run-over passes. rlhe two pieces of material thus further attenuated, as they come from the run-over passes are pulled apart, placed together again and doubled. That is to say they are folded on the transverse mid-line, and so are made into a pack of four sheets. rl"his pack is returned to the same furnace in which the roughed bars were reheated, and when brought to roll ing temperature again, is taken from the furnace and passed twice through the mill. These passes which constitute the third rolling step are called the fours. After this the pack is again opened, that is to say, the component sheets are pulled apart from their free toward their folded edges and adhesions are broken. The pack then is doubled again and becomes a pack of eight sheets. This pack at one end consists o t four free sheets four sheets With folded edges. rlhe pack at this end then is sheared7 so that the edges of all the eight sheets are at this end free. The pack is reheated, and then is passed through the mill from three to tive times, and in these passes which constitute the 'fourth rolling step, called linishing passes7 the hot-rolling` is completed. lThe rolled pack is sheared and cut. and the component sheets are torn apart. In the tearing apart the sheets are necessarily more or less mutilated., and many are on account of adhesions and mutilations rejected.

The operation cf hot rolling is attended by danger to the rolls; danger of breaking, and danger of the development of small cracks ranging from T17 inch to g5? inch deep. These cracks cevering the surface of the roll gf. e to it superiicially a crazing on approximately cubically disposed planes of cleavage, the cubes ranging` from about l@ inch to 578 inch in size.

l/Vhen a roll breaks the entire train of mills has to be stopped and considerable time is lost. The value of the roll Will be from $400.00 to 35700.00, and the loss in production may total one to tivo hours for six to eight mills, so that it is very costly. In addition, each of such stops entlang/1ers every other roll in the other mills. .llhe rolls used range from 28 inches to inches in diameter and from 30 inches to Se inches long. they are made of cast iron with a chilled surface and are very hard. The metal has practically little or no elasticity. 'llhe high temperature ol 750o to 900o or 1000O l?. at which they work means considerable expansion, and as the temperature cannot be uniiorni throughout theicast ing, the .metal ot necessity under coni-rider able stress at all times. .ils an example, when the rolling` operation. begins, the surface metal ot the roll is expanded both cireinniierd entially und lonnitiulinally, and as the heal: penetrates expansion ijiroinesses trom the surface inward. it such accession ot heat be too rapid the roll will be 'tracturedat the center. and dueto the inelastic nature of the material the shock will continue the 'fracture to thesuriiiace, and the roll will be broken in tivo at about its middle. 1n other Words, the `roll Will be pulled apart at the center when the tension of the expandino` outer metal becomes greater than the tens-aile .strength ot the unex panded core.

When a thorouglrhly heated and equally ein panded roll is stopped heat begins to `be radiated, .and an opposite etlect takes place. ln this case it the surface metal which tirst contracts and its contraction, resisted by the still expanded center, brings about a condr ition of tension. lil the contraction be slou7 enough, so that the tensile strength of the `cooler parts is not exceeded, nothing; happens.; but it the (.:ontraetion be a little too `fast, numerous fractures deep enough to give relief to strain. appear in the suritace. As such contraction and tension involve all ot `the superlicial portions ot the roll, so will the smallicraolrs (termed erasing) be distributed; and since the tension is about equal both around an dlenuthivise ot the roll.. the crazing takes a cubic term, trom cracks running lengthwise caused by tension around its cir oumterence, and orar-.hs running around the roll caused by tension lengthwise of its bar rel. Those running' around the roll are nu- Inerous, and in proportion to the ratio ot the `lempgtli oit the barrel of the roll to its diameter. Such crazinor occurs when rolls heated `to a temperature oit about '7000 or more are allowed to cool in the open air. lllhen rolls are hotter and are allowed to contract faster, or when some rapid means ot couiluctin,if away the heat are applied to the 'tace of a noli, the contraction becomes so rapid that one or more cracks are produced ot considerable depth and lenu'th running around `the roll. They may be from a halt an inch deep and six or seven inches lone up to seven to ten inches deep and include halt the circumn terence. Such a oracle .may completely tracture the roll a t once. but it it does not` the crack soon grows to a complete fracture by being' torn deeper and lonu'cr each time the roll is subjected to the strains ot rolling. These cracks are called tire craclrs and are responsible 'tor prat .cally all broken rolls. The exceptions are very ten'. ln actual prac- 4broken duringl the tinishii moons? tice roll breakage is proportionate to roll length. The strains are kgreater as roll length increa., and the strains are greater as the range oit temperature increases, and the teniperuture ranges increases as (thicker and hotter packs are rolled. rlhe matter is :tin-ther complicated by the greater spring` in longer rolls, due to longer distance between bearings, and by such increase in strain as is incident to the rollingr oi" a` larger and more cunil'iersome pack.

ln the practice oit rolling' sheets 'tor tinninn', the bars are roughed at a temperature of M00O to llliOO; the matching.)Y passes and the 'tours are rolled at about 13000; and the material goes through the finishing' passes at about 1200o F. rlhc roughing is done very quickly; all the bars ina heat, say twenty to twenty-tour pairs, are put through in eight or ten minutes, and, because ot the higrh temperature et the material, the rolls then reach their maximum temperature. The rolling o't `the matching` passes and ot the tours is accomplished with relatively little consumption olf time. and with little diniinution oli' roll temperature. ln the h'nishing passes. however, .much more time is consumed, because ot' the greater length which the material has attained. The actual passage through the mill consumes more time. and the material because ot toe attenuated torni which `it has assumed requires more caretul handlingl and slower handling by the mill crew. And time is lost. in other \.vays-in measuring the length et the pack, tor exonuple. ln consequence, there is a 4ureater teinperature drop (ilurinol the tinishinpy step than during' any other part et the rolling' operation. rlhe n'iaterial enters the [inishinp: pass at about 1200o F. `and is finished at about i000o l?. This fourth or i'inishinp: step el the rolling' operation is the step during' which the rolls are in greatest jeopardy. rll`he pack then is relatively thin and cold, and the rollingl pressure `is many times greater than at the beginning'. Rolls are inost frequently in* step in the rollinel operation` and brealaue occurring at other times is oiten properly attrilnitable to injury which the roll has sustained in the finishing step upon a preeedin.u1 heat or run ot' material. lilllhen, as Otten happens.y the continuity ot mill operation is interrupted for a longer or shorter period ot time. the rolls cool and then when rolling* is resumed they are peculiarly liable to breakn troni tire crack caused by contraction duringthat period.

In practicing; my invention l prrn"` shield covering the roll surface to the er possible extent. rilhe shield serves pr to protect the roll trom drat'ts and curre ot outside air. l provide with the shield ineaiis tor blowino; t-hrtv h it and upon the surface ot the roll streams ot air or other gaseous fluid of properly regulated temper ture. rlhus radiation of heat from the roll surface may be controlled and arrested, or even a condition of absorption of heat by the roll may be set up.

In Fig. I of the accompanying drawings the rolls l of a three-high mill are shown in end elevation, carried in the housing 2. The shields to which I have alluded are indicated at 4f. The arrangement of the shields with respect to the rolls more clearly appears in Fig. III, and in Figs. III-VI the structure of the shields is shown in detail. The shields in cross-section are crescent-shaped, the inner curve conforms to the curvature of the roll surfaces; they are spaced from the roll surfaces at a slight interval, and they extend circumferent-ially around the roll surfaces. It will be understood that they extend longitudinally of the roll, preferably from end to end. So much of the roll may thus be shielded as is conveniently possible, without interference with other features of structure and operation.

The shields are hollow; they are provided with conduits 40, enteringl through the rear walls, through which air (or other suitable gas) may be blown, and the shields may be faced with foraminate plates ell, through which the in-blown air may be spread, as it flows out upon the surfaces of the rolls. The shields may be divided interior-ly into chambers arranged in succession longitudinally of the roll and the conduits 40 may lead to the several chambers. The dividing partitions l2 between the chambers may at their out-er edges and adjacent the roll surfaces be Zigzagged, and as the ldrawings indicate, the partitions may extend outwardly beyond the face plates 4l of the shields, and to nearer approach to the roll surfaces. By such provision streams of air to effect. heating or cooling or retardation of heating or of cooling may be directed upon the surfaces of the rolls. Such streams may be concentrated upon the mid-areas in the length of the roll, or they may alternately be concentrated upon areas toward the ends of the roll bodies. And by vvirtue of the zig-Zag shape of the partitions the localized effect of streams of air upon the roll body may toward the edges of theareas played upon be caused to grade gradually away. Hot or cold air or other gaseous iiuid may be supplied to the shields by any well-known and preferred means. Additionally or alternatively the shields themselves may be provided with hot elements such as electrically heated coils 43, arranged adjacent the roll surfaces and constituting roll heating means.

In operation cold air may be blown upon the surface of the roll as it rises from contact with the relatively hot material in the roll pass, an-d the cold air may be so blown upon the roll surface, in such quantities and at such temperature and during suoli portion of the path of revolution, that the heat taken up by the roll surface in the roll pass will immediately be taken away, and will notl penetrate the roll body more deeply. And course the play of such a cooling stream upon the roll surface will not be continued beyond the point necessary or for a time greater than that necessary, to carry away the excess heat and to maintain the roll otherwie at substantially the desired normal temperature. 'lfhe flow of such a cooling stream may obviously be brought under automatic control, so as to act upon the roll during those periods of time only when the roll carries accretions of heat. That is to say, sequent upon the advance of the material from the roll pass and the relief of the strain of rolling, the supply of such cooling streams of air will be cut ofi'.

In contrast to such a cooling stream, streams of hot air may by the means indiated and described flow over the roll surface at such times as may be desired. At times when the rolling operation is intermitted the rolls may by means of the heating elements described be for indefinite lengths of time maintained at rolling temperature, or even by such means they may initially be brought to rolling temperature.

I have already explained that the greatest danger to the rolls is that due to cooling, at the time of the fourth or finishing step of the sheet rolling operation. Having provided the shield of my invention, particularly if it be adapted to deliver a stream of hot air upon the roll surface, I am able to prevent cooling of the roll during this step, and so to relieve the danger. And in addition, the rolls may be maintained hotter at this time, and in consequence the packs under rolling operation may be kept hotter. T he working of the material may thus be made easier, and particularly the good end is gained, that the outside sheets of the pack will then be rolled more nearly to the same length as the inside sheets.

rlhe roll of a mill in operation tends to become hottest at the mid-point in its length, and to expand most at that point. It is for this reason that rolls are turned to a diameter which diminishes slightly from ends to middle, so that in operation the roll body will become more perfectly cylindrical. .But a chilled roll does not manifest throughout its life an invariable response to thermal conditions; a'lter each successive heating there is less contraction toward the initial dimensions. t is on this account that new and old rolls cannot be successively matched together. Then a new pair of rolls goes into service only narrow paclismay be rolled, because of the then maximum etlect ofthe turning of the roll, with diminished diameter toward the mid-point in its length. As the rolls grow CII hotter, the width of the packs may be increased, until the Ytull width is reached. This maximum width may be maintained tor a linie, and then the rolls begin to .manifest ,erreaiei' wear away toward the iniddle. rlhis is because ot the tact that toward its` uiiddle the roll is hottest. The Width et the pack rolled inust then be reduced in. ily the adoption oit the shields in which niy invention centers, and by operatingl thoin iu the manner .l have described, it is possible to turn the rolls initially to more perfectly cylin- (lrical l'torni and, by control et heating; and cooling; streams, to maintain 'through periods ot tune exeeedinil earlier possibilities, this substantially portee t cyl indrieal Vtorni. ltaiclrs oli ulaxiinuni Width may be rolled with a given pair ot rolls throufggh longer periods oit service. with economy ot operation and increase ot tonnage. 'lho rolls properly turned inay be so mounted es not to touch at any part, and in consequence a better roll surface niey be niaintained, and this through longer periods oit service.

liv so controlling and inaintaining;l roll ilinineter it becomes possible to introduce the baro and paclrs to the roll passes at soinowhat lower temperature than present-day practice requires, und still to operate with such expedition that at the completion ot the operation the material is hotter than in the presentday practice it noiv remains; it becomes possible to roll packs of greater width, and` handling' the material meclninically in place oi manually, to roll packs ot greater length, a n d packs composed oit n greater nu1nber ot sheets. ln place ot a pack ot eig'lit sheets oit the present niaiiniuin permissible size ot 28 X i2 in ches, it becomes entirely practicable to roll a peel: of twenty sheets 56 x ,Lt/l inelies. .lhe consequent gains in speed and mill capacity, in re luction in the number oi reheatiinrs, in uniiforinity oit product, in reduction oi" the number oit surface sheets, in reduction in the quantity ot waste and scrap and trinnninns-all this, apart troni the economies ol" ineclianieal distinguished 'trom manual Feedingr.,--boco1nes apilnn'ent.

ln the rolling' of high grade sheets it i desiralile to roll at as lonv a temperature a possible, in order to reduce to a ininirnuni th amount of scale toi-ined and also to avoid as completely as possible tearing, sliveringr, linlringi', etc. caused by sticking'. lilith the rolling' ot relatively cooler patchs, as is the case in the practice ot my invention, the rolls do .not reach so high a tenipera'ture, and :troni the standpoint oit reduction and elongation as well as the equal leinth ot the surtace sheets it would be more desirable that the rolls be hotter, giving' a kenner v tors terni it. '.lhis desiral'ile end may be at tained by usino the heatinoj elen'ient ot iny invention, even while rolling; paclrs ot' lovv teinperature. Such use of the heating' element inill as ope/ram will not interiter "ith inaintenanceof the proper sha-pe ot the rolls, as that i'iiitiiiteiniiiee of shape is governed by the blowing of huinid air, as described. llie two :features of the heater element and the inblovvn stream ot nir will then be in operation at the saine time. My invention so tar as concerns the thermal condition ot' the rolls aecordino'ly lends itself to the mechanical lianifllingr or the material, and the invention is realized in its perfection .in a inill in. which the inovisions concerning' roll temperature are eonibined 'ivith provis ions for handlingg` larger and heavier' units.

The invention as thus tar described eenters in the shield, troni which air or other inay be blown, to keep the rolls While in service frein becoming too hig'hiy heated, a shie d composed oi' compartments, troni any one or niore ot vhieli air may be blown, to

lreep the roll in certain portions frein X- i pending too greatly and to maintain a particular optimum contour; a shield which se ens the .roll and protects it Jfrom outside drafts or currents oit air, and which, enclosing the roll and icontining an envelope of air next `to the roll surface, prevents rapid radiution oit heat and consequent too rapid contract-ion oi' the exterior portions of the roll body upon a still rela-tively hot and expanding` interior portion; n. shield equipped With heating' means arranged adjacent the roll surface, for the purpose, first, ot initially heating` the roll before the rolling` operation begins; second, of heating; differentially one portieri ot the roll body relatively to another While the rolling' operation is in progress, and so maintaining al desired roll cont-enr; third, et raising the body of the roll to a temperature higher than that to which it otherwise would be brought, fourth, of keeping the roll hot and oi maintaining it in proper sha-pe during intervals nf'hen the roll ing; operation is interrupted; and, finally, of helping to etiect gradual contraction when the rolling operation has been completed.

ln Fig. l, l shon7 associated with the rolls oi the rolling inill conveyor tables ior the mechanical handling olf the material in course oi' rolling'. Such mechanical handling apparatus is in its general tentures known. iParticular tentures orQ the apparatus shown are niade the subject-matter of a companion ap plieation Ytor Letters Patent, tiled March 17, 1927, Serial No. 176,082. lt suffices here to indicate that by the use et such mechanical niateriail-handling apparatus the economies consequent upon the control oit roll toniperature as described above may be realized in largest measure.

l claini as my invention l. ylhe incthod ot rolling herein described comprising' maintaining within the body oi.E a roll oit :i hot-niill a condition of better uniformity ot ten'iporaturo by causing a stream of coolingl fluid to play upon the surface of the roll as the surface recedes from the surface or the article being rolled and cutting otl' the iiow of the stream When the article being` rolled gasses from beneath the action of the roll7 and passing,` the article to be rolled through said rolls the temperature ol" Which has been tuus regulated.

2. lhe method of rolling herein described comprising maintaining` Within the bodies of the cooperating rolls of a hot-inill conditions of better uniformity of temperature by causi streams of cooling` liuid to play simultaneously noon the surfaces or the rolls as the surfaces recede from the surfaces of the article being rolled and cutting olif the flow of the streams when the article being rolled passes from the roll pass, and passing the article to be rolled through said rolls the temperature of which has been thus regulated.

ln a rolling mill and in combination with a roll body of an elongate box crescentshaped in cross-section and including inner and outer curved Walls different in radius et curvature, the inner Wall of the crescentsliaped lion corresponding in curva .gre to Ythe roll surface, and being 'perfor-ate, and the box beingIv arranged with the said inner Wall in proximity to the roll surface7 and means for maintaining Within the box al supply o'l temperature-controlling luid.

et. The structure of claim 3, together with a heatingl element arranged between the inner Wall of the box and the roll surface.

5. The structure of claim 8, together with a partition extending transversely and in Zigzag course Within the box.

6. ln a rolling mill and in combination With a roll body of a shield extending circuinferentially of and longitudinally of and adjacent to the roll body, the shield being box-like in structure opening toward the surface of the roll7 a partition extending in devious course Within the shield and dividing the space Within into independent chainbers arranged in succession longitudinally of the roll, and means for causing gaseous .streams to flow through the said chambers and over the outer surface of the roll body.

7. In a rolling mill and in combination with a roll body, two elongate boxes extending longitudinally of and circumferentially or" the roll and arranged on opposite sides ot' the roll7 each box being divided internally into a succession of chambers longitudinally ot the roll, the Wall of the bonr adjacent the roll surface being pertorate, and means for supplying' streams ot temperature control ling' fluid through the box and to the roll surface.

In testimony whereof I have hereunto set my hand.

WALTER R. KNEELAND. 

